Erstad was last seen at approximately 7:30 p.m. on June 1, 1992 as she went to play in Skyline Park near her family's residence in Inver Grove Heights, Minnesota. Her father told authorities that Erstad's two older brothers walked to the park to bring her back home after she had been gone for approximately five minutes. The child was nowhere to be found and has never been heard from again. Erstad's mother and stepfather reported her as a missing person two hours after she was last seen.

A child playing in the park told authorities that he believed he saw Erstad speaking with an unidentified man during the evening. The boy said that he saw a girl matching her description petting the man's dog. It has never been verified that the girl was in fact Erstad.

Authorities viewed Erstad's family's friend Robert Guevara as the main suspect in her disappearance from the onset of their investigation. Guevara often stayed overnight at the family's home at their invitation when he was intoxicated. Witnesses told authorities that Guevara often slept in the same bed as Erstad. Erstad's mother, Mona Williams, stated her daughter had accused Guevara of molesting her on the day of her disappearance. Williams did not tell the police about this until several days after the child disappeared; she claimed she had forgotten about the incident until then. Guevara was at Erstad's home the day she was reported as a missing child, and police dogs tracked her scent to his home after her disappearance. He was charged with her kidnapping, rape and murder on June 5, 1992, four days after Erstad disappeared.

Authorities discovered a dress identical to the garment Erstad was last seen wearing and a pair of girl's underpants inside Guevara's locker. The items of clothing had been stained with blood and semen. Bloodstains were also discovered on a shower curtain inside Guevara's trailer. DNA testing showed that the fluids could have come from both Erstad and Guevara. Defense witnesses argued at Guevara's trial that his locker and trailer were not secured and that the evidence could have been planted by unknown person(s) in order to frame Guevara for Erstad's disappearance.

Guevara's attorneys theorized that Williams wanted to sell her daughter or arrange for her kidnapping to collect the anticipated ransom. Erstad's home life was troubled. Her family moved frequently, their only income came from welfare payments, and Williams had been treated for cocaine abuse and emotional problems.

Minnesota law did not allow full usage of DNA evidence at trials in 1992; the law has since been revised. As a result, Guevara was acquitted of all charges in connection with Erstad's case. He has continued to maintain his innocence throughout the years.

Erstad's case remains unsolved, although she was declared legally dead in 1994. She has never been located.